This invention relates to a process and apparatus for the selective separation of non-ferromagnetic metals from a mixture of comminuted metallic scrap having an approximately uniform particle size. Such a mixture arises during the processing of so-called shredder-scrap. Generally such scrap is comminuted and non-metallic constituents are removed, ferromagnetic constituents being then selectively separated by a magnetic process whereby finally a mixture of non-ferromagnetic particles of relatively uniform size after the removal of additional particles of predetermined sizes.
Heretofore, such mixtures of non-ferromagnetic metals, particularly those consisting of relatively small particles, were of minimal commercial value because their lead content was disproportionately high despite the previous separation steps and also because the separation of various metals contained in the mixture, mainly lead, zinc, aluminum and copper or copper and zinc in the form of brass, could not be achieved economically or because the final materials obtained by these processes did not possess sufficient purity needed for economical use. These mixtures could, however, be used as additives in certain cases. Considering the ever increasing industrialisation and the growing shortage of raw materials the importance of recycling is also greater. It has thus become increasingly necessary and also more profitable to extract pure metals from all kinds of scrap.
Various methods are presently known for extracting certain metals from scrap, particularly scrap consisting of larger particles. Thus, it has been known to melt certain metals out of mixtures by the use of radiant heat, and to selectively apply heat according to the melting points of the metals to be extracted. However, in addition to the fact that poisonous metal oxides could be generated due to reaction with the oxygen of the air, the degree of purity of metals obtained by these controlled heating techniques is extremely unsatisfactory because a portion of the melted metal remains as a coating on the non-molten metal. A similar problem arises with a known process in which the metallic mixture is introduced into a bath having a higher temperature than that of the melting point of the metal to be extracted because here also the efficiency of the process in terms of the quantity of the selected metal extracted from the remaining mixture is unsatisfactory.
Based upon this state of the art it is one object of the invention to provide process and apparatus, which permits the continuous separation of selected non-ferromagnetic metallic constituents from scrap mixtures at a relatively high throughput rates even when the particle size of the mixture is relatively small. The financial costs of the process must be maintained sufficiently low so that the extracted metals can be sold competitively. It is also important that there be minimum adverse effect upon the quality of the environment, a factor which has become more and more important.